[aat] Add m grave test (#1412)

test/shaping/data/in-house/tests/macos.tests

 # 10.12.6
+/System/Library/Fonts/Helvetica.dfont@c7bec2785a4c402b7809b5e35337c3d24c18e281::U+006D,U+0300:[m=0+1706|gravecmb=0@-284,10+0]
+/System/Library/Fonts/LucidaGrande.ttc@d89a9d7e57767bfe3b5a4cfd22bb1e9dbe03a062::U+006D,U+0300:[mgrave=0+1912]
 /System/Library/Fonts/Times.dfont@39c954614d3f3317b28564db06d5b7b7a6ff0e39::U+0066,U+0069:[fi=0+1139]
 /Library/Fonts/Khmer MN.ttc@5f5b1072df99b7355d3066ea85fe82969d13c94a::U+17A2,U+1780,U+17D2,U+179F,U+179A,U+1781,U+17D2,U+1798,U+17C2,U+179A:[km_qa=0+1025|km_ka=1+1025|km_sa.sub=1+517|km_ro=4+593|km_vs_ae=5+605|km_kha=5+1025|km_mo.sub=5+0|km_ro=9+593]
 /Library/Fonts/Tamil MN.ttc@37a2020c3f86ebcc45e02c1de5fdf81e2676989d::U+0BA4,U+0BCA,U+0B95,U+0BC1,U+0B95,U+0BCD,U+0B95,U+0BAA,U+0BCD,U+0BAA,U+0B9F,U+0BCD,U+0B9F,U+0BC1:[tgm_e=0+1702|tgc_ta=0+1598|tgm_aa=0+1149|tgc_ku=2+1962|tgc_k=4+1592|tgc_ka=6+1592|tgc_p=7+1370|tgc_pa=9+1370|tgc_tt=10+1596|tgc_ttu=12+1833]
@@ -12,6 +14,8 @@
 /System/Library/Fonts/SFNSDisplay.ttf@92787c30716672737e9059bc367c15d04fbc1ced::U+0056,U+0041,U+0056,U+0041:[gid265=0+1227|gid4=1@-65,0+1162|gid265=2@-65,0+1162|gid4=3@-65,0+1227]
 
 # 10.13.6
+/System/Library/Fonts/Helvetica.ttc@8a928f9866299d2455f41360202b7a3b48503a5e::U+006D,U+0300:[m=0+1422|gravecmb=0@0,96+283]
+/System/Library/Fonts/LucidaGrande.ttc@63ba1b1de4709bd832ca76bd62368dd99fc34269::U+006D,U+0300:[mgrave=0+1912]
 /System/Library/Fonts/Times.ttc@896098b6979306ad84355025459f7c68b029139c::U+0066,U+0069:[fi=0+1139]
 /Library/Fonts/Khmer MN.ttc@782ba6cf3fca0512ab348dfe08345a2d5dc5bf2c::U+17A2,U+1780,U+17D2,U+179F,U+179A,U+1781,U+17D2,U+1798,U+17C2,U+179A:[km_qa=0+1025|km_ka=1+1025|km_sa.sub=1+517|km_ro=4+593|km_vs_ae=5+605|km_kha=5+1025|km_mo.sub=5+0|km_ro=9+593]
 # The following is broken https://github.com/harfbuzz/harfbuzz/issues/1410